1. Field of the Invention
The present invention relates to an image display field, and more particular to a crucible of a coating machine
2. Description of Related Art
The organic electroluminescence device is a self-emitting device with low voltage, wide viewing angle, quick response speed, temperature adaptability and other advantages, and it is a new generation of the display technology.
From the point of view of the molecular mass of the organic electroluminescence material, the organic electroluminescence device can be divided into the organic electroluminescence device with small molecular mass (OLED) and the organic electroluminescence device with large molecular mass (PLED). Because the molecular mass is different, the manufacturing process is also great different. The OLED is mainly manufactured through thermal evaporation method, and the PLED is manufactured by spin coating or inkjet printing method.
The thermal evaporation method is mainly heating the organic material in a vacuum environment (E−5 Pa) so that the sublimation type or the melt type organic material is vaporized at high temperature, and is depositing on a substrate having a thin film field effect transistor TFT structure or an anode structure. The evaporation source is mainly divided into a point type evaporation source or a linear type evaporation source. The point type evaporation source is small in space, and a coating chamber can install many point type evaporation sources so that it can fill a variety of materials inside the coating chamber. The point type evaporation source is mainly used in an experimental production line and an early mass production line. Since the material utilization rate and the thickness uniformity of the linear type evaporation source are better than the point type evaporation source, most of mass production line constructed recently utilizes the linear evaporation source.
The difference of the evaporation temperature and the degradation temperature of the organic material is very small. The temperature difference in the interior of the crucible with the point type evaporation source is usually larger (hot at the upper portion and cold at the lower portion). If the amount of the material filled into the chamber is larger, the material cannot reach a steady state of thermal equilibrium so that the evaporation rate cannot be stabilized. If it increases the temperature to make the material reach a steady state of thermal equilibrium, it often causes the material at the upper portion to be in the risk of degradation. If the amount of the material filled into the chamber is less, at high evaporation rate, the temperature at the upper portion of the crucible often exceeds the degradation temperature of the material, and the vaporized material is easy to degrade.
To solve the above problem, it often utilizes thermal conductive balls. It mixes the thermal conductive balls when the organic material is filled in the crucible. Through the heat conduction of the thermal conductive balls, it makes the temperature of the material uniform. However, the above method is only useful for the sublimation type material. The melt type material is melted at a high temperature, and because the density of the thermal conductive balls is different from the density of the organic material, the thermal conductive balls will be gradually deposited on the bottom of the crucible such that they cannot conduct heat well.